This invention relates to proximity sensing systems and methods. Such systems and methods are useful for managing power consumption in an electronic device, as well as for other purposes.
Power management is becoming increasingly important as electronic devices place greater reliance on battery power. Portable computers, personal data assistants (PDAs), tablet computers, cellular phones, pagers, and wireless computer peripherals are only a few examples. While components of such devices are becoming increasingly power hungry, the demand for longer intervals between battery replacement or recharging has increased. Indeed, many devices are often turned on for ready usability but left idle for significant periods of time. Accordingly, there is an increasing need for systems and methods that reduce or slow battery depletion.
Wireless peripheral devices intended for use with a host computer are becoming more common. In particular, cursor control (pointing) devices such as a computer mouse can be made wireless by inclusion of a battery power source within the device and providing a wireless data link to a personal computer or other device via, e.g., an infrared or RF transmitter/receiver pair. Without effective power management, however, continuously operating a wireless peripheral can rapidly deplete the device""s battery power, thereby requiring frequent battery replacement or recharging.
A common method of minimizing power consumption is to configure a device to xe2x80x9csleepxe2x80x9d when it is not being used. In other words, a device may turn off many of its components during periods of non-use, and turn those components back on when the device is used. In a wireless computer mouse employing mechanical encoder wheels moved by a roller ball, sleep can occur by powering down the mouse""s transmitter and receiver components, as well as other components not currently needed. The mouse can then periodically sample the encoder wheels for movement. When a change is detected in encoder wheel position between sampling intervals, the device xe2x80x9cwakes upxe2x80x9d and reactivates any powered-down components. This sampling occurs at a rate that is fast in comparison to human response time (on the order of 50 millisecond (msec) intervals); moving the mouse thus xe2x80x9cwakesxe2x80x9d the device without a perceptible delay. After experiencing a designated period of no motion, the mouse can then go back to sleep. The inactive intervals between sampling allow the average power use during xe2x80x9csleepxe2x80x9d to be very small.
In another line of technological development, cursor control devices utilize optical surface tracking systems in lieu of conventional encoder wheel arrangements. Exemplary optical tracking systems, and associated signal processing techniques, include those disclosed in commonly owned U.S. Pat. No. 6,172,354 (Adan et al.) and copending applications Ser. No. 09/692,120, filed Oct. 19, 2000, and Ser. No. 09/273,899, filed Mar. 22, 1999. Optical tracking can provide more reliable and accurate tracking by eliminating moving parts (e.g., a ball and associated encoder wheels) which are prone to malfunction from the pick-up of dirt, oils, etc. from the tracked support surface and/or a user""s hand. On the other hand, optical tracking requires considerable power for driving the circuitry used to illuminate a trackable surface and to receive and process light (image information) reflected from the trackable surface.
Although optical mice and other cursor control devices are an improvement over devices relying upon mechanical encoder wheels, sampling mouse motion as a method of xe2x80x9cwakingxe2x80x9d a sleeping optical mouse is problematic. To determine motion, the imager must be powered and compare at least two successive images to determine motion. This requires a motion detector""s illuminating LED to be turned on for a significant amount of time. The resultant power use is thus greater than that of a sleeping mechanical mouse. There is thus a need for alternative methods and systems that sense when a mouse (or other input device) is needed and wake the device. Proximity detection is one such alternative. Instead of sampling the mouse""s (or device""s) motion detector elements for movement, detection of a user""s approaching hand can be used as an indicator that the mouse must wake up.
Various types of user proximity detectors are known and used in power management systems and other applications. For example, Mese et al. U.S. Pat. No. 5,396,443 discloses power saving control arrangements for an information processing apparatus. More specifically, the Mese et al. patent describes various systems for (1) detecting the approach (or contact) of a user associated medium to (or with) the apparatus; (2) placing a controlled object of the apparatus in a non-power saving state when such contact or approach is detected; and (3) placing the controlled object in a power saving state when the presence of the user associated medium (i.e., a stylus pen or part of a user""s body) is not detected for a predetermined period of time. The ""443 patent describes various types of approach/contact sensors. Among these, various xe2x80x9ctabletxe2x80x9d type sensor systems are described, including electromagnetic, capacitance, and electrostatic coupling tablets. In one embodiment, a contact or approach detecting tablet, and a flat display panel, may be integrally formed with a housing of the information processing apparatus.
Sellers U.S. Pat. No. 5,669,004 discloses a system for reducing power usage in a personal computer. More specifically, a power control circuit is disclosed for powering down portions of a personal computer in response to user inactivity, and for delivering full power to these portions once user activity is detected via one or more sensors. The components to which power is reduced (or removed) are components which can respond almost immediately to being turned on. On the other hand, components which require a period of time to come up to full operation (e.g., disk drive motors, monitor, main processor) are driven to full power. In the primary embodiment that is disclosed, the sensor is a piezoelectric sensor fitted into a keyboard. Sellers discloses that sensors may be positioned at other locations on the computer (a monitor, mouse, trackball, touch pad or touch screen) and that various other kinds of sensors (capacity, stress, temperature, light) could be used instead of piezoelectric sensors.
Commonly owned U.S. patent application Ser. No. 09/948,099, filed Sep. 7, 2001, discloses capacitive sensing and data input device power management systems and methods. In the disclosed embodiments, capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a xe2x80x9cscoopxe2x80x9d capacitor formed by a conductor and surrounding ground plane. The conductor may be a plate provided in the form of an adhesive label printed with conductive ink. Charge is transferred between the scoop capacitor and a relatively large xe2x80x9cbucketxe2x80x9d capacitor, and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition from low to high (or high to low) of the input threshold is detected, and a value indicative of the number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or in contact with a device can be determined by comparing the value with a predetermined threshold. The predetermined threshold can be adjusted to take into account environmentally induced changes in capacitance of the scoop capacitor.
The present invention provides a simple system and method for proximity detection representing an alternative to the capacitive sensing systems and methods described in Ser. No. 09/948,099. The invention is described by way of a particular implementation in a wireless computer mouse using optical tracking, but can be implemented in other forms and in other contexts. The invention detects proximity of a hand, other body part or other object by measuring output from a phototransistor or other device that generates, in response to an electromagnetic illumination, a voltage or other output that varies with time of illumination. When electromagnetic radiation from an adjacent illuminating source is reflected by an object into the receptor, the output of the receptor rises more quickly than the output would rise in response to ambient conditions alone. The output is sampled at multiple points during a sampling period, and an indication of the relation of each sample to a threshold value is recorded. To compensate for detector output rise over time that would occur in ambient conditions (i.e., with no reflected energy from the adjacent illumination source), two series of samples are recorded. The first series is taken in ambient conditions (the illuminating source off), and the second series is taken with the illuminating source activated. The sequence of recorded output indications from the xe2x80x9conxe2x80x9d series is compared to the sequence of recorded output indications from the xe2x80x9coffxe2x80x9d series, and if the change is above a designated level, an object is determined to be near.
In one embodiment of the invention, a phototransistor (PTR) is used as a receptor, and an infrared light emitting diode (IR LED) is used as an illumination source. A series of bits is recorded with the IR LED off, with a xe2x80x9c0xe2x80x9d bit stored for each sample where the PTR voltage is below a threshold voltage and a xe2x80x9c1xe2x80x9d stored for each sample where the PTR voltage is at or above the threshold voltage. A second series of bits is recorded with the IR LED on, and the results compared. If the difference in xe2x80x9c1xe2x80x9d bits is above a designated level, an xe2x80x9cobject-nearxe2x80x9d condition has occurred (i.e., object is recognized to be near).
According to another aspect of the invention, a second sensor (e.g., a second receptor/illuminating source pair) is added, and an object-near condition is not recognized unless both sensors detect the object. In this manner, false detections can be avoided when a user device (e.g., a computer mouse) is positioned next to a stationary object (e.g., a coffee cup or other desktop object). According to another aspect of the invention, the voltage sample series can be tested for noise or other anomalous results, and the series discarded if corrupted.